The following background description is provided to assist the understanding of the reader. None of the information provided or references cited in this background section is admitted to be prior art to the present invention.
Fuzes for explosive projectiles often receive programming information from a message coil in a projectile launcher that uses alternating current (AC) signals through inductive transfer to a receiver coil in the fuze to receive the message. This inductive message transfer device is often referred to as an inductive setter. In some fuzes, power may be extracted from the AC message to power the fuze, charge capacitors, or combinations thereof.
FIG. 1 illustrates a fuze circuitry used to extract power from an inductive setter 10. The AC signal on from the inductive setter 10 feeds a rectifier 20 including a full-wave diode bridge rectifier for converting the AC signal to a DC signal 25. A capacitor 30 may be used to filter the rectified voltage to create a more stable DC signal. The DC signal may drive fuze power circuitry 40 that may further condition and regulate the DC signal to provide power at varying loads to the fuze electronics. Excess power not used by the fuze power circuitry 40 may be captured by a capacitor in a capacitor charging circuit 50. The capacitor charging circuit 50 may provide power to the fuze electronics after the messaging has completed and the inductive setter 10 is no longer providing an AC signal. Generally, in such a configuration, the power output from the inductive setter 10 must be maintained at or below a specified average power level.
However, the energy storage capacitor starts to charge from zero volts, which appears as a virtual short circuit to a DC power source. As a result, current to the capacitor 30 must be limited to avoid exceeding the average power limit of the inductive setter 10. Previous designs limited the current to the capacitor 30 to a preset constant value until the storage capacitor was fully charged.
FIG. 2 illustrates a constant current power ramp 80 to a storage capacitor. Line 60 indicates a power limit for the inductive setter 10 (FIG. 2). As the capacitor voltage increases over time and with constant current, the power going into the capacitor increases linearly as illustrated by line 80 and reaches its maximum power level only when the capacitor is fully charged at time 70. Actual energy captured by the storage capacitor is illustrated by shaded area 90. Thus, the inductive setter 10 outputs its power limit 60 only at the very end of the capacitor charging period, limiting the energy capture efficiency to only 50%.
In addition, as the fuze load changes during the setting operation, (e.g., components are powered down after their data transfer is complete) there is no redirection of available energy to the storage capacitor. This means that the constant current value must be conservatively set at a level to account for the maximum fuze power draw, even though this may only occur over a brief portion of the entire setting operation.
There is a need to improve the efficiency of power delivery to charge storage devices and fuze electronics with power supplies and power needs that vary over time.